1. Field of the Invention
This invention relates to a vehicle equipped with at least one internal combustion engine having a means to control the rate of flow of fuel to the engine in operation.
A vehicle having road wheels driven by an internal combustion engine the operation of which is entirely controlled by the driver of the vehicle can be driven in such a manner as to use excessive amounts of fuel, to exceed legal speed limits, and incur excessive wear to the engine, the braking system, tires and other parts of the vehicle. It is therefore an object of the present invention to provide means capable of automatically preventing a driver from causing a motor vehicle to exceed a predetermined speed.
Motor vehicles are known which have an internal combustion engine of the injection type which uses diesel oil or gasoline and consequently has a fuel pump for controlling the rate of flow of fuel to the engine, the vehicle being equipped with power take-off apparatus which can be driven by this engine. There is, however, a difficulty involved in the use of the power take-off apparatus of such a vehicle in that the control over the rate of flow of fuel given by the usual manual or foot control arrangement for the fuel pump is very coarse in the middle range of the speed of rotation of the engine output shaft. FIG. 1 of the accompanying drawings shows an example of engine speed in r.p.m. against fuel input for an injection engine. It will be seen that control is good at low and high r.p.m. but very difficult in the range between 1,000 r.p.m. and 2,000 r.p.m.
2. Brief Summary of the Invention
It is an object of the present invention to provide means to overcome this difficulty in a way which does not involve the use of very complex and expensive fuel pumps which, while being satisfactory for power take-off requirements, are detrimental to the road performance of the vehicle where the engine is the engine which drives the powered road wheels of the vehicle. However, the invention is not limited to use in connection with vehicles employing injection engines for driving power take-off apparatus but applies whether the engine is either of the injection type of has other means controlling the flow of fuel to the engine, and applies whether or not the engine which is used to drive the power take-off apparatus is the same engine which drives road wheels of the vehicle.
In accordance with the invention, means are provided for sensing rotation of an output shaft driven by said engine and producing in response thereto a repetitive signal in which the duration of the repeated element is inversely related to the speed of rotation of the said output shaft. Electrical control means coupled to the sensing means receive the repetitive signal and are coupled to the means for controlling the rate of supply of fuel. These electrical control means are such that in use whenever the duration of the said repeated element becomes less than a predetermined duration when the speed of rotation of the said output shaft is increasing from zero, the electrical control means operate so that the means for controlling the rate of supply of fuel responds by reducing the rate of supply of fuel. The electrical control means are also such that the means for controlling the rate of supply of fuel does not allow the rate of supply of fuel to increase or be increased after the duration of the said repeated element becomes less than the said predetermined duration until the duration of the repeated element increases through a larger predetermined duration. Furthermore, the electrical control means may be such that whenever the of rotation of the said output shaft exceeds one or more further higher predetermined values after exceeding a first predetermined value corresponding to the first said duration the means for controlling the rate of supply of fuel responds thereto by further reducing the rate of supply of fuel.
The means for controlling the rate of supply of fuel may include a hand or foot operated member operable to control the rate of supply of fuel whenever the speed of rotation of the said output shaft is below the first said predetermined value.
Preferably, the means for sensing rotation of the said output shaft and producing in response thereto a repetitive signal is such that the repetitive signal consists of a stream of pulses.
Where the repetitive signal is a stream of pulses, the electrical control means may be such as to produce a binary signal which changes from one level to the other level in response to the speed of rotation of the said output shaft exceeding the said predetermined value. The binary signal can be used to effect energisation or de-energisation of electrical means so coupling the electrical control means to the means for controlling the rate of supply of fuel that a reduction in the rate of supply of fuel is effected by the means for controlling the rate of supply of fuel whenever the said electrical means is energised, or alternatively whenever the said electrical means is de-energised. The said electrical means may comprise a relay having a set of contacts which control the supplying of electrical power to a solenoid comprising a part of the means for controlling the rate of supply to fuel.
In a preferred embodiment in which the sensing means produces a streams of pulses, the electrical control means includes an astable multivibrator so coupled to the sensing means as to be inhibited for a predetermined interval at each pulse produced by the sensing means. Such coupling may include a switching device arranged to short-circuit a timing capacitor of the astable multivibrator in response to each pulse from the sensing means. Consequently if the pulse repetition rate exceeds the value at which the astable multivibrator is just able to begin a cycle of its astable operation, the astable multivibrator is inhibited, i.e. locked in one state. The astable multivibrator is so coupled to a monostable circuit in the preferred embodiment that the monostable circuit is triggered to or maintained in its set state by each occurrence of that part of the cycle of operation of the astable multivibrator which occurs only when the astable multivibrator is not inhibited. Consequently the monostable circuit is set and remains set when the astable multivibrator is not permanently inhibited, i.e. when the pulse repetition rate of the sensing means is low enough to allow at least part of a cycle of astable operation of the astable multivibrator to occur between the leading edges of each pair of successive pulses produced by the sensing means. When the pulse repetition rate of the sensing means is too high for this to occur, the astable multivibrator locks in a state which results in the monostable circuit returning to and remaining in its reset state while the multivibrator is thus locked. An output signal from the monostable circuit representative of the state of that circuit is thus a binary signal which changes from one level to the other level in response to the speed of rotation of the said output shaft exceeding the said predetermined value when increasing from zero.
In this preferred embodiment, a further switching device is provided for determining for which one of two possible values of the said predetermined interval the astable multivibrator is inhibited before carrying out its astable operation. The further switching device may, for this purpose, be arranged to short circuit, when closed, part of the resistance in the timing circuitry of the astable multivibrator. The further switching device is so controlled by the binary output signal of the monostable circuit that the astable multivibrator can carry out its astable operation after the shorter of the two inhibit intervals whenever the monostable circuit is in its set state, and vice versa. Consequently the rate of rotation of the said output shaft for which the monostable circuit is set again after being reset is a lower rate than the rate for which the monostable circuit is reset. This difference between the rates provides hysteresis in the controlling action of the electrical control means and prevents hunting.
Other advantageous features of the present invention will be better understood from the following description given by way of example with reference to the accompanying drawings.